PASADENA, Calif. — The international Cassini spacecraft has taken new images of Saturn’s two-faced moon Iapetus, possibly offering clues to why the moon has a dark hemisphere and another that is bright, scientists said Thursday.

The spacecraft took pictures of Iapetus (pronounced eye-APP-eh-tuss) at a distance of 1.8 million miles on July 3, a few days after Cassini entered orbit around Saturn.

Iapetus is one of Saturn’s 31 known moons and has a diameter about a third that of Earth’s moon. It was discovered in 1672 by the Italian-French astronomer Jean Dominique Cassini.

One theory is that the dark side is being coated by particles being ejected from Saturn’s tiny moon Phoebe. Another theory is that the material comes from within the moon, an idea supported by observation of material on crater floors.

Cassini is the first spacecraft to orbit Saturn. The $3.3 billion mission is a joint project of NASA and the European and Italian space agencies.